One particularly effective method I found to ferret-proof a fireplace
involved Plexiglass.  I had a piece of Plexiglass cut to the size of the
fireplace opening, and then used black duct tape to tape it in place.  This
worked well since the framing around the fireplace was black metal.  In
fact, once I was done, it was very unobtrusive.  As soon as I was done, the
ferrets seem to completely forget about the fireplace, and no one noticed
that the front was Plexiglass just from looking at it.
 
Of course, this isn't particularly effective if you want to use your
fireplace, but it's a good summer solution, at least.
 
--Stevi &
        Nusa - just try keeping me out of the closet!
        Fresno - just leave me a sock or two around to nibble on!
[Posted in FML issue 2467]